Division of Agricultural Sciences and Natural Resources • Oklahoma State University

FoliagediseasesofconiferscanbeofgreatimportancetothesurvivalandgeneralvigorofthesetreesinOklahoma.Thegreenneedlesofconifersoftenrepresentseveralyearsofgrowthandthetreedependsuponalloftheseneedlesforitsphotosyntheticneeds. Coniferswillremaingreenthroughouttheyearbygradu-allysheddingtheolderinnerneedlesandatthesametimeproducingnewneedlesfromthetipsofthebranches.Unlikebroadleaf, deciduous trees that completely replace only aportionoftheirneedles.Completedefoliationofconifersisoftenfatal.Evenpartialdefoliationcanresult inunhealthy,disfiguredtreesbecauseappreciablelossofneedlesisnotfollowedbyacompletereplenishmentofthefollowingyear. Coniferdiseasesareofmosteconomic importancetohomeownersduetotheoff-colorofinfectedfoliageandthepoorappearanceofthetree.InordertoassisthomeownersandcommercialgrowerstounderstandseveralofthemoreimportantconiferdiseasesthatoccurinOklahomaandtheircontrols,thefollowingdiseaseswillbediscussed:DothistromaNeedleBlight,DiplodiaTipBlight,NeedleCasts,PhomopsisBlightofJunipers,CedarAppleRust,andPinewoodNematodeDisease.

Dothistroma Needle Blight of Pines Dothistroma Needle Blight can cause the prematureloss of needles of several varieties of pine. In Oklahoma,DothistromaNeedleBlighthasbeenrecordedfromAustrian,PonderosaandMughopines.Thisdisease,ifuncontrolledforseveralyears,canseverelyweakenandeventuallykillthesetrees.

Symptoms Symptomsdevelop in thefallof theyear inwhichtheinfection was initiated. Early symptoms consist of yellowandtanspots,andwater-soakedbandsontheneedles.Thebandsandspotsmayturnbrowntoreddishbrownandmaybesurroundedbyyellowbands.thetipsoftheneedleswilldie,withthebaseoftheneedlesremaininggreen.Thedeadportion of the needle may break off leaving a blunted tip.Extensivedamagemayoccurontheneedleswithintwotothreeweeksoftheinitialappearanceofsymptoms.Infectedneedleswillbeshedorcastfromthetreeprematurely.UnderOklahomaconditions,needlefallisextensivefollowinghot,drysummers.(Figure1.)

Disease Cycle ThenonsexualstageofthefungusDothistromapiniistheonlystagefoundinOklahoma.Conidia(spores)ofthefungusareproducedinstromata(amassoffungalmyceliuminoronwhichsporesare formed) in thespotsandbandsontheneedles.Thestromatabegintoforminthefalloftheyear,butmostmaturetoproduceconidiaduringthefollow-ingspring.Conidiaarespreadbyrainsplashthroughoutthegrowingseason(May-October).Infectionoccursthroughoutthegrowingseason,butsymptomsdonotdevelopuntillatesummerorearlyfall.Twoseasonsarerequiredforcompletionofthediseasecycle.

Control Copper fungicides (Bordeaux mixture 8-8-100, Tenn-Cop5E,orCopperFungicide4E)effectivelycontrolDothis-troma Needle Blight. Two applications are recommended,thefirstinmid-Maytoprotectthepreviousseasons’needlesandthesecondinmid-JunetoJulytoprotectthecurrent-yearneedles.Inaddition,homeownerscanhelpcontrolthisdiseasebycollectingtheinfectedneedlesanddestroyingthem.

Diplodia Tip Blight

Symptoms Thisfungaldiseasecanseriouslyattackpineseedlingsinnurseries,causingarotthatstartsbelowthesoillineinthecollarareaofthestemandextendsupwardintothemainstem.Thescalesofyoungconesarealsoattacked.Thisdiseasealsocausesadiebackofthebranchesofolderpinetrees.Growthfromtheseblightedterminalsisusuallystunted,theneedlesturnbrown,andtheterminalbudsexudeanexcessiveamountofresin(Figure2).Diplodiacanalsoinfecttheconesoftheseolderpinesandtheminuteblackfruitingbodiescaneasilybeseenonthescalesofthecones(Figure3).

Disease Cycle Diplodia pinea infects the plants through the youngneedles.Infectiontakesplacethroughsmallopeningsintheneedlescalledstomates. Infectioncanalsooccur throughwoundsandcracksinthebark.

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OklahomaCooperativeExtensionFactSheetsarealsoavailableonourwebsiteat:

http://osufacts.okstate.edu

Common Diseases of Conifers in Oklahoma

KennethE.ConwayResearchPlantPathologist

BrianOlsonPlantDiseaseDiagnostician

Oklahoma Cooperative Extension Service

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Figure 1. Dothistroma needle blight on Austrian pine.

Figure 2. Stunted terminal branch of pine infected with Diplodia pinea.

Figure 3. Pine cones infected with Diplodia pinea. The small black dots on the pine cone scales are fruiting bodies of this fungus.

Figure 4. Juniper seedling infected with Phomopsis blight.

Control Seedlingsandyoungtreesthatareinfectedwiththestemrotphasecannotbetreatedsuccessfully.WhenDiplodiaTipBlighthasbeenaprobleminseedlingproduction,theuseofsteam-pasteurizedsoilorsoilfumigantswillhelpincontrollingrootandsteminfection. DiplodiaTipBlightonoldertreescanbecontrolledbypruningandsanitation.Assoonasblighted terminalsandconesarenoticed,theneedles,twigsandconesshouldbeprunedtohealthytissueanddestroyed.Donotprunewhenthebranchesarewetbecausetheconidiaofthefunguscaneasilybespreadwhenmoistureispresent.Whereinfectionhasbeensevere, theuseofBordeauxmixtureorCopperFungicide4Ewillcontrolthisdisease.Itshouldbeappliedearlyinthespring,whenthebudsopen,andtwicemoreatweeklyintervalsuntiltheneedlesbreakthroughtheneedlesheaths.Anapplicationoffungicideinthefallmayalsoaidinslowing thespreadof thedisease;however, fertilizationandwateringinthefallmaybemorebeneficial.HomeownerswhomaintainvigoroustreesthroughgoodtreehealthcarewillhavefewerproblemswithDiplodiaTipBlight.

Needle Casts

Symptoms Thefirstindicationofthistreediseaseisthescorchedbrownoryellowishappearanceofmostoftheneedles.ManypinesareaffectedbythisdiseaseanditcanbecomeasevereprobleminChristmastreeplantings.Theinitialdiscolorationoftheneedlesisfollowedbyneedlefallorcasting.Fewtreesareactuallykilledbythisdefoliationbutsustainedneedlekillwilleventuallyreducetheoverallgrowthrateandmakethetreemoresusceptibletootherdiseasesandinsectattack.Over40differentspeciesoffungiarecapableofcausingneedlecase.ThemoreimportantonesareLophodermium pinastri,Hypoderma lethale,andHypoderma hedgcockii.

Disease Cycle Small blackelliptical fruitingbodiesof the fungusareproducedontheneedles.Thesestructuresbreakopeninthelatespringorearlysummerduringperiodsofwetweatherandreleasegreatnumbersofspores.Thesporescanbespreadbysplashing rainorwind to infectotherneedlesor trees.

Infectedneedlesbegintoturnbrownduringthelatefallandearlyspringandwillhaveamottledappearanceduetothedeathofneedletissueattheinfectionsites.Temperatureandhumidityareveryimportantindeterminingtheseverityoftheinfection.

Control Innurseriesthisdiseasecanbecontrolledbytheapplica-tionofthefungicideaftertheneedlesarehalfgrownfollowedbyasecondapplicationwhentheneedlesarefullydeveloped.Nochemicalcontrolmeasuresarenormallyrecommendedforhomeownerseventhoughthetreemayappearunsightly.Collectionofinfectedneedlesandtheirdestructionwillgreatlyreduce this disease. However, if a homeowner wishes tocontrolthisdisease,theproperapplicationofafungicidewillprovideexcellentcontrol.

Phomopsis Blight of Junipers Thisisthemostcommondiseaseofcedar,juniper,andarborvitaeinOklahoma.PhomopsisBlightcanbeasevereprobleminnurseryplantingsandcancausethedeathofmanyseedlings.OldertreesarelessaffectedbyPhomopsisBlightandunless these treesareenvironmentallystressedor inpoorhealththeyareusuallynotaffectedenoughtowarrantchemicalsprays.

Symptoms and Disease Cycle Infectedtreeswillexhibitbrowningofthefoliageanddyingoftwigsandbranches(Figure4).Smallblackfruitingbodiesofthefungus,Phomopsis juniperovora,areformedonthisdeadtissue.Conidiaareproducedinthesestructuresandwhenmoistureispresentmassesofconidiawilloozeouttoformtendrilsorhorns.Theconidiaarespreadbyrainandvariousothermeanssuchasmechanicaldisruptionandinsects.Thefungusenterstheplantthroughwoundsaswellasunbrokentissue.Thebrowningoftheneedlesandtwigsbeginsatthetipsandprogressesdownwardtowardthestem.Moistureisanimportantfactorindiseasespreadandseverity.NurseriesandChristmastreeplantationsthatutilizeoverheadirrigation

usuallyhavemoreseverediseaseproblemsbecausewettingofthefoliageresultsinearlierspreadoftheconidia.

Control Goodsanitationisimportantinreducingdiseaseoccur-renceinnurseries.Cleancultivation,gooddrainageandroguingareimportanttechniquesthatshouldbefollowed.Fungicidesareusuallyappliedasprotectantsandaregularscheduleoffungicidespraysmustbeappliedtopreventthepenetrationofthefungusintotheplants.Homeownersareencouragedtouseatleasttwosprays,oncewhenthediseaseisfirstnoticedandanother10to14dayslater.Forbestcontrol,infectedtwigsshouldbeprunedpriortotheapplicationofthefungicide.

Cedar Apple Rust ThisdiseaseisverycommononjuniperorcedartreesinOklahoma.Themoststrikingfeatureofthisdiseaseisthegall thatappearsonthecedar inthespring.Long,orange,gelatinous tendrils or horns develop from these galls andhomeownerscaneasilyrecognizethesestructuresandknowthatthisdiseaseisactive.Thesegallscanbeprunedbythehomeownerbeforethehornsareformedtoachievecontrolofthisdisease.FormoreinformationconcerningthisdiseaserefertoOSUExtensionFactsEPP-7611,CedarAppleRust.

Pinewood Nematode Disease of Pines In1972,Japanexperiencedseverewiltingproblemsinpineforests.Theproblemwasfinallyidentifiedasbeingcausedby a nematode, Bursaphelenchus xylophilus. A JapanesescientistvisitinginMissouriinthespringof1979recognizedthesamesymptomsonpinesinthatstate.LaterthediseasewasreportedfromKansas,Arkansas,Oklahoma,andIllinois.InOklahoma,thediseasehasbeenfoundasfarwestasGradyCounty.

Symptoms Thediseaseistypifiedbytherapiddeathofthepinetree.ifthewoodiscutfromthesetrees,thewoodwillbedryandnopitchflowwillbenoted.Thesesymptomsshouldnotbeconfusedwiththeslowdeclineofpinesthatmayresultfromdrought conditions. Needles of drought stressed trees willturnbrownanddie,butthetreemayputonnewgrowth,andpitchwillflowwhenthewoodiscut.Severalspeciesofpines

havebeeninfectedbythisnematodedisease.However,inOklahoma,onlyAustrian,Scotch,andJapaneseblackandredpinehavebeenfoundtobeinfected.

Disease Cycle Thenematodehasacloserelationshipwithawoodbor-ingbeetlesometimescalledalong-hornbeetle.Whenadultbeetlesemergefrominfectedtreestheycarrythenematodeswiththemintheirtracheae(airtubes).Thebeetlesthenenteryoungtendertissueofhealthypineswheretheyfeed.Thenematodesleavethebeetlesandenterthewoodthroughthewoundsmadebytheinsect.Theymigratetotheresincanalsandfeedontheepithelialliningofthesecanals.Thenema-todes reproduce rapidly (insummer,onegenerationeveryfivedays).As thepopulationsbuildup, thewilt symptomsbegintoappearandwithinafewweeksthetreedies.Duringthewinter,thenematodelarvaeaccumulatebeneaththetreebarkaroundthechambersofpupatinginsectlarvae.Whentheinsectsmolttotheadultstage,thenematodesalsomoltandenterintothespiracles(airopenings)oftheinsectstostartthecycleagain.

Control 1. Sanitation-Onalocalbasis,astreesarediagnosedas

being infectedwith thepinewoodnematode, the treesshouldberemovedanddestroyedasquicklyaspossible.Sanitationwillbemoredifficultinlargeforestedareas.

2.Chemical Control -Insecticidespraystocontrolthelong-hornbeetlevectorwouldbefeasibleinsmalllocalitiesiftheseverityofthediseasewarrantsthattypeofcontrol.InJapan,valuableforestareashavebeensuccessfullytreatedbyaerialapplicationofinsecticides.

3.Resistant Cultivars -The Japanese have developedsome promising pine selections that appear to be re-sistanttothenematodes.TheUniversityofMissouriatColumbiaisalsotestingthehostrangeofthenematodetohelpdeterminesourcesofresistanceinournativepinetrees.

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Figure 1. Dothistroma needle blight on Austrian pine.

Figure 2. Stunted terminal branch of pine infected with Diplodia pinea.

Figure 3. Pine cones infected with Diplodia pinea. The small black dots on the pine cone scales are fruiting bodies of this fungus.

Figure 4. Juniper seedling infected with Phomopsis blight.

Control Seedlingsandyoungtreesthatareinfectedwiththestemrotphasecannotbetreatedsuccessfully.WhenDiplodiaTipBlighthasbeenaprobleminseedlingproduction,theuseofsteam-pasteurizedsoilorsoilfumigantswillhelpincontrollingrootandsteminfection. DiplodiaTipBlightonoldertreescanbecontrolledbypruningandsanitation.Assoonasblighted terminalsandconesarenoticed,theneedles,twigsandconesshouldbeprunedtohealthytissueanddestroyed.Donotprunewhenthebranchesarewetbecausetheconidiaofthefunguscaneasilybespreadwhenmoistureispresent.Whereinfectionhasbeensevere, theuseofBordeauxmixtureorCopperFungicide4Ewillcontrolthisdisease.Itshouldbeappliedearlyinthespring,whenthebudsopen,andtwicemoreatweeklyintervalsuntiltheneedlesbreakthroughtheneedlesheaths.Anapplicationoffungicideinthefallmayalsoaidinslowing thespreadof thedisease;however, fertilizationandwateringinthefallmaybemorebeneficial.HomeownerswhomaintainvigoroustreesthroughgoodtreehealthcarewillhavefewerproblemswithDiplodiaTipBlight.

Needle Casts

Symptoms Thefirstindicationofthistreediseaseisthescorchedbrownoryellowishappearanceofmostoftheneedles.ManypinesareaffectedbythisdiseaseanditcanbecomeasevereprobleminChristmastreeplantings.Theinitialdiscolorationoftheneedlesisfollowedbyneedlefallorcasting.Fewtreesareactuallykilledbythisdefoliationbutsustainedneedlekillwilleventuallyreducetheoverallgrowthrateandmakethetreemoresusceptibletootherdiseasesandinsectattack.Over40differentspeciesoffungiarecapableofcausingneedlecase.ThemoreimportantonesareLophodermium pinastri,Hypoderma lethale,andHypoderma hedgcockii.

Disease Cycle Small blackelliptical fruitingbodiesof the fungusareproducedontheneedles.Thesestructuresbreakopeninthelatespringorearlysummerduringperiodsofwetweatherandreleasegreatnumbersofspores.Thesporescanbespreadbysplashing rainorwind to infectotherneedlesor trees.

Infectedneedlesbegintoturnbrownduringthelatefallandearlyspringandwillhaveamottledappearanceduetothedeathofneedletissueattheinfectionsites.Temperatureandhumidityareveryimportantindeterminingtheseverityoftheinfection.

Control Innurseriesthisdiseasecanbecontrolledbytheapplica-tionofthefungicideaftertheneedlesarehalfgrownfollowedbyasecondapplicationwhentheneedlesarefullydeveloped.Nochemicalcontrolmeasuresarenormallyrecommendedforhomeownerseventhoughthetreemayappearunsightly.Collectionofinfectedneedlesandtheirdestructionwillgreatlyreduce this disease. However, if a homeowner wishes tocontrolthisdisease,theproperapplicationofafungicidewillprovideexcellentcontrol.

Phomopsis Blight of Junipers Thisisthemostcommondiseaseofcedar,juniper,andarborvitaeinOklahoma.PhomopsisBlightcanbeasevereprobleminnurseryplantingsandcancausethedeathofmanyseedlings.OldertreesarelessaffectedbyPhomopsisBlightandunless these treesareenvironmentallystressedor inpoorhealththeyareusuallynotaffectedenoughtowarrantchemicalsprays.

Symptoms and Disease Cycle Infectedtreeswillexhibitbrowningofthefoliageanddyingoftwigsandbranches(Figure4).Smallblackfruitingbodiesofthefungus,Phomopsis juniperovora,areformedonthisdeadtissue.Conidiaareproducedinthesestructuresandwhenmoistureispresentmassesofconidiawilloozeouttoformtendrilsorhorns.Theconidiaarespreadbyrainandvariousothermeanssuchasmechanicaldisruptionandinsects.Thefungusenterstheplantthroughwoundsaswellasunbrokentissue.Thebrowningoftheneedlesandtwigsbeginsatthetipsandprogressesdownwardtowardthestem.Moistureisanimportantfactorindiseasespreadandseverity.NurseriesandChristmastreeplantationsthatutilizeoverheadirrigation

usuallyhavemoreseverediseaseproblemsbecausewettingofthefoliageresultsinearlierspreadoftheconidia.

Control Goodsanitationisimportantinreducingdiseaseoccur-renceinnurseries.Cleancultivation,gooddrainageandroguingareimportanttechniquesthatshouldbefollowed.Fungicidesareusuallyappliedasprotectantsandaregularscheduleoffungicidespraysmustbeappliedtopreventthepenetrationofthefungusintotheplants.Homeownersareencouragedtouseatleasttwosprays,oncewhenthediseaseisfirstnoticedandanother10to14dayslater.Forbestcontrol,infectedtwigsshouldbeprunedpriortotheapplicationofthefungicide.

Cedar Apple Rust ThisdiseaseisverycommononjuniperorcedartreesinOklahoma.Themoststrikingfeatureofthisdiseaseisthegall thatappearsonthecedar inthespring.Long,orange,gelatinous tendrils or horns develop from these galls andhomeownerscaneasilyrecognizethesestructuresandknowthatthisdiseaseisactive.Thesegallscanbeprunedbythehomeownerbeforethehornsareformedtoachievecontrolofthisdisease.FormoreinformationconcerningthisdiseaserefertoOSUExtensionFactsEPP-7611,CedarAppleRust.

Pinewood Nematode Disease of Pines In1972,Japanexperiencedseverewiltingproblemsinpineforests.Theproblemwasfinallyidentifiedasbeingcausedby a nematode, Bursaphelenchus xylophilus. A JapanesescientistvisitinginMissouriinthespringof1979recognizedthesamesymptomsonpinesinthatstate.LaterthediseasewasreportedfromKansas,Arkansas,Oklahoma,andIllinois.InOklahoma,thediseasehasbeenfoundasfarwestasGradyCounty.

Symptoms Thediseaseistypifiedbytherapiddeathofthepinetree.ifthewoodiscutfromthesetrees,thewoodwillbedryandnopitchflowwillbenoted.Thesesymptomsshouldnotbeconfusedwiththeslowdeclineofpinesthatmayresultfromdrought conditions. Needles of drought stressed trees willturnbrownanddie,butthetreemayputonnewgrowth,andpitchwillflowwhenthewoodiscut.Severalspeciesofpines

havebeeninfectedbythisnematodedisease.However,inOklahoma,onlyAustrian,Scotch,andJapaneseblackandredpinehavebeenfoundtobeinfected.

Disease Cycle Thenematodehasacloserelationshipwithawoodbor-ingbeetlesometimescalledalong-hornbeetle.Whenadultbeetlesemergefrominfectedtreestheycarrythenematodeswiththemintheirtracheae(airtubes).Thebeetlesthenenteryoungtendertissueofhealthypineswheretheyfeed.Thenematodesleavethebeetlesandenterthewoodthroughthewoundsmadebytheinsect.Theymigratetotheresincanalsandfeedontheepithelialliningofthesecanals.Thenema-todes reproduce rapidly (insummer,onegenerationeveryfivedays).As thepopulationsbuildup, thewilt symptomsbegintoappearandwithinafewweeksthetreedies.Duringthewinter,thenematodelarvaeaccumulatebeneaththetreebarkaroundthechambersofpupatinginsectlarvae.Whentheinsectsmolttotheadultstage,thenematodesalsomoltandenterintothespiracles(airopenings)oftheinsectstostartthecycleagain.

Control 1. Sanitation-Onalocalbasis,astreesarediagnosedas

being infectedwith thepinewoodnematode, the treesshouldberemovedanddestroyedasquicklyaspossible.Sanitationwillbemoredifficultinlargeforestedareas.

2.Chemical Control -Insecticidespraystocontrolthelong-hornbeetlevectorwouldbefeasibleinsmalllocalitiesiftheseverityofthediseasewarrantsthattypeofcontrol.InJapan,valuableforestareashavebeensuccessfullytreatedbyaerialapplicationofinsecticides.

3.Resistant Cultivars -The Japanese have developedsome promising pine selections that appear to be re-sistanttothenematodes.TheUniversityofMissouriatColumbiaisalsotestingthehostrangeofthenematodetohelpdeterminesourcesofresistanceinournativepinetrees.

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Ifyouhavenoticedpinetreesthathavediedrapidly,weurgeyoutosubmitsamplestothePlantDiseaseDiagnosticLaboratory foranalysis.Rapid removalof these treesmayslowthespreadofthediseaseandreduceitsseverity.

General Recommendations Manyofthesediseaseswillinfectweakenedtreesmorereadilythanhealthytrees.Goodtreecareincludingwateringduring drought conditions, fertilization, insect control, and

properpruningwilleliminateor reducediseaseproblems.Sanitation,whichmeans thecollectionanddestructionofdiseasedplantparts,isaneasyandeconomicalmethodforhomeownerstousetoreducetheirdiseaseproblems.Whendiseaseissevereorvaluableornamentalsmustbeprotected,theuseoffungicideswillgiveexcellentcontrol.Theratesoffungicidetobeusedcanbefoundonthelabel.BesuretoREAD THE LABEL CAREFULLY andfollowanylimitationsandotherinstructionslisted.

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IssuedinfurtheranceofCooperativeExtensionwork,actsofMay8andJune30,1914,incooperationwiththeU.S.DepartmentofAgriculture,RobertE.Whitson,DirectorofCooperativeEx-tensionService,OklahomaStateUniversity,Stillwater,Oklahoma.ThispublicationisprintedandissuedbyOklahomaStateUniversityasauthorizedbytheVicePresident,Dean,andDirectoroftheDivisionofAgriculturalSciencesandNaturalResourcesandhasbeenpreparedanddistributedatacostof42centspercopy.0803